How does prone y strengthen the lower trapezius, amnd how do i get the lower traps working, do i focus on rotating the scapular upwards to get my arms up or purely by bringing the shoulder blades together.
all answers will be greatly appreciated
Pull the shoulder blades together aggressively, that should do the trick.
Isometric holds are a great option.
Lay face down on an incline bench, and shrug. The key is to start really light and the movement should feel like you are pulling up and back. Think of pulling your shoulder blades into the opposite back pants pocket.